The present invention relates to communications systems and more particularly to packet switching equipment called fast packet switching whereby data and real time digitized analog information are transmitted in limited length self addressed information packets.
One very common type of communications system is time division multiplexing and time-space-time switching. See, for example, AT&T Technical Journal, Volume 64, No. 6, Part 2, August 1985, and Gordon et al., U.S. Pat. No. 3,749,845. In such a system, a large number of endpoints are connected to a central switch which switches a fixed bandwidth from one endpoint to another. Connections are made at call initiation by a central processing unit and call arbitrator. Multiplexing and switching of the fixed bandwidth circuits can be distributed through the use of many switches and multiplexers arranged in tree structures.
Fixed bandwidth communications channels can provide for both digitized voice and data transfer. Data transfer, however, typically requires protocols at the endpoints of the circuit outside the network to ensure an orderly, efficient and understandable communication between data terminals.
An improved prior art scheme for transmission of data is revealed in A. G. Fraser, U.S. Pat. No. 3,749,845. In this system, transmission occurs with the use of limited, but variable, length information packets. Each packet contains all information required to direct itself to the proper endpoint. This information includes flow control information, error detection, sequencing, line protocol, and session control. The parts of the packet which contain this information will hereinafter be called overhead fields and will be referred to generally as overhead.
The packets of information can generally vary in length from approximately 10 bytes to over 1024 bytes of data. Fields containing the overhead information change length, structure and identity depending on the information contained therein. Because of the complex structure of the packet, the packets are switched at switching points with the use of computer processors. Processors identify, store and route packets from switch to switch and ultimately to their final destination.
An important characteristic of this communication system is that the protocol of the transmitting station is generally unchanged at the receiving station. Another characteristic is that switching and transmission require complex computer processing of the data packets. These characteristics limit the speed of end-to-end communications because of the need for processors running communications protocol software. Other characteristics are that prior art equipment based on this technique is non-deterministic, has too great a communication delay, and is too slow for voice or video applications.
Modifications of this system are found in two systems for communicating in a local environment described in Metcalfe et al., U.S. Pat. No. 4,063,220 and Janson et al., U.S. Pat. No. 4,482,999. These systems use packet switching techniques within a line protocol which allows many stations to communicate by contending for a single transmission media. They do not rely on a single switch or arbiter to control transmission and therefore the failure of any station will not cause a failure of the entire network. While these systems provide flow control and other transport, network, and line protocols, they typically do not provide session support or presentation protocol support and, therefore, do not allow dissimilar terminals, processors and computers to communicate with each other directly without other protocol conversion equipment or software present. Moreover, since these systems also use computer processors and software processes to perform communications functions of flow control and error control, end-to-end transfer of data is relatively slow.
Another prior art scheme is exemplified in the papers S. R. Amstutz, "Burst Switching - An Introduction", IEEE Communications, November 1983 and E. F. Haselton, "A PCM Frame Switching Concept, Leading to Burst Switching Network Architecture" IEEE Communications, September 1983. This system has the ability to switch both voice and data in a common media. It allows for efficient multiplexing of fixed bandwidth channels for short periods of time by switching variable length packets traveling on 64 kilobit per second time division segments of a 1.5 megabit per second transmission line. After the end of a packet has passed, any other station may use the 64 kilobit per second segment. However the system does not handle the various transport protocols necessary for efficient end-to-end data communications. Moreover, since the system operates by switching fixed time segments of one or more 64 kilobit per second bandwidth channels, it does not lend itself well to digitized analog or data transmission where the speed of transmission is either greater or less than 64 kilobits per second.
Lastly, a prior art scheme known as fast packet switching exemplified by Turner, U.S. Pat. No. 4,491,945 is able to handle voice and data traffic in the same packet format and therefore overcomes many of the problems of previous methods. This method uses a Banyan type switching element to route data from beginning to destination. Packets travel along high speed transmission lines which are distance independent. Generation rates determine the bandwidth used in the system. However, Turner's system is very complex and requires high density VLSI integrated circuits. It requires many address translations as the packets travel within the system requiring elaborate set up procedures and consequently long session start up times. The system does not provide a method to achieve multiple sessions for an individual endpoint, nor does it address the problem of protocol conversion. It also requires the use of computer processors to provide the large amount of software protocol necessary for efficient data communications. Finally, Turner's system is not able to handle high bandwidth video or data traffic.
One problem posed by the prior art is the inability to simultaneously handle both data and digitized voice and video transmissions. Another problem is the intensive use of computer processors to perform data communications which severely limits the speed of data transmission and precludes the use of these processors to perform tasks other than data transmission such as protocol conversion. Another problem is the inability to allow comprehensible and meaningful communication between data terminals and computers of different types. Other problems include the inability to handle high speed data transfer, the inability to provide end-to-end session level encryption of voice or data, and the lack of a facility for providing multiple sessions or conversations to a single endpoint or using device.